1. Field of the Invention
The present invention relates to fuel cell.
2. Description of the Related Art
There has been the urgent demand of higher performance and durability for fuel cells, especially polymer electrolyte fuel cell (PEFC) which is expected as the future power source in the field of stationary or transportation use from the environmental point of view. However this demand has not been attained by the present time, because its technological problems were mainly derived from the essential technological problems described below.
The electric power is generated by feeding the anode gas of hydrogen or hydrogen containing gas into the anode gas flow field and the cathode gas of air or oxygen containing gas into the cathode gas flow field respectively. The power is controlled by the amount of both the gases, that is, the feeding rates into the gas flow fields have to be in proportion to the loading level needed for its consumption power. When the feeding rate is increased, the gas pressure drop from inlet to outlet through the gas flow field is tremendously increased, since the gas flow plate has a long serpentine gas flow field. This means that the higher pressure drop increases the consumption of electricity for the cathode gas or fuel feed pump resulting in the low efficiency of the energy. Furthermore, this means that the time to reach the steady state of a certain gas feeding rate is far from the needed one for the response to the change of needed power resulting in the further low efficiency of the energy.
When the feeding rate is decreased, water flooding occurs in the anode and cathode gas flow fields by the remaining water not to be expelled by the increase of the gas velocity through the gas flow field. The influence of water flooding is seriously appeared in the cathode site, because of the production of water is produced at the cathode according the reaction (2).Anode: H2→2H++2e  (1)Cathode: 1/2O2+2H++2e→H2O  (2)Total: H2+1/2O2→H2O  (3)
This water flooding has been considered as one of essential harmful failure mode for the performance of PEFC resulting in the drop of operation voltage and poor life performance. Therefore, the new technology to compensate both phenomena of water flooding at the low power load and high pressure drop at the high power load in the wide range is strongly demanded for the practical use of PEFC.